arXiv subjects

L. Schmidtobreick

Publications and source records attributed to L. Schmidtobreick.

54 records · Page 3Linked to original sources

arXiv2007

K-band spectroscopy of pre-cataclysmic variables

We have taken K-band spectroscopy of a sample of 13 pre-CVs in order to examine them for anomalous chemical abundances. In particular, we study the strength of the 12CO and 13CO absorption bands that have been found diminished and enhanced, respectively, in similar studies of CVs. All our systems show CO abundances that are within the range observed for single stars. The weakest 12CO bands with respect to the spectral type are found in the pre-CV BPM 71214, although on a much smaller scale than observed in CVs. Furthermore there is no evidence for enhanced 13CO. Taking into account that our sample is subject to the present observational bias that favours the discovery of young pre-CVs with secondary stars of late spectral types, we can conclude the following: 1) our study provides observational proof that the CO anomalies discovered in certain CVs are not due to any material acquired during the common envelope phase, and 2) if the CO anomalies in certain CVs are not due to accretion of processed material during nova outburst, then the progenitors of these CVs are of a significantly different type than the currently known sample of pre-CVs.

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arXiv2007

VSOP: The Variable Star One-shot Project I. Project presentation and first data release

The Variable Star One-shot Project (VSOP) is aimed at (1) providing the variability type and spectral type of all unstudied variable stars, (2) process, publish, and make the data available as automatically as possible, and (3) generate serendipitous discoveries. This first paper describes the project itself, the acquisition of the data, the dataflow, the spectroscopic analysis and the on-line availability of the fully calibrated and reduced data. We also present the results on the 221 stars observed during the first semester of the project. We used the high-resolution echelle spectrographs HARPS and FEROS in the ESO La Silla Observatory (Chile) to survey known variable stars. Once reduced by the dedicated pipelines, the radial velocities are determined from cross correlation with synthetic template spectra, and the spectral types are determined by an automatic minimum distance matching to synthetic spectra, with traditional manual spectral typing cross-checks. The variability types are determined by manually evaluating the available light curves and the spectroscopy. In the future, a new automatic classifier, currently being developed by members of the VSOP team, based on these spectroscopic data and on the photometric classifier developed for the COROT and Gaia space missions, will be used. We confirm or revise spectral types of 221 variable stars from the GCVS. We identify 26 previously unknown multiple systems, among them several visual binaries with spectroscopic binary individual components. We present new individual results for the multiple systems V349 Vel and BC Gru, for the composite spectrum star V4385 Sgr, for the T-Tauri star V1045 Sco, and for DM Boo which we re-classify as a BY Draconis variable. The complete data release can be accessed via the VSOP web site.

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arXiv2007

The Variable Star One-shot Project, and its little child: Wikimbad

The Variable Star One-shot Project (VSOP) aimed at providing to the world-wide stellar community the necessary one-shot spectrum of unstudied variable stars, too often classified as such by an analysis of photometric data only. The VSOP has established an new kind of observational model, where all steps from observations to spectral analysis, are automatized (or are underway to be fully automatized). The project is centralized on a collaborative wiki website. The VSOP operational model is very successful, data is continously flowing and being analyszed, and VSOP is now a worldwide open collaboration of people with very different and complementary skills and expertise. The idea of a central wiki website has been extended by one of us to propose a new service to the whole astronomical community, called Wikimbad. Wikimbad is an open wiki website aimed at collecting, organizing and making publicly available all kind of reduced and published astronomical data. Its strengths and a comparison with the Virtual Observatory are discussed. See: http://vsop.sc.eso.org and http://wikimbad.org

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arXiv2006

Spectroscopic search for new SW Sextantis stars in the 3-4 hour orbital period range -- I

[Abridged] We report on time-resolved optical spectroscopy of ten non-eclipsing nova-like cataclysmic variables in the orbital period range between 3 and 4 hours. Of the ten systems so far observed, HL Aqr, BO Cet, AH Men, V380 Oph, AH Pic, and LN UMa are identified as new members of the SW Sex class. We present improved orbital period measurements for HL Aqr (Porb = 3.254 +- 0.001 h) and V380 Oph (Porb = 3.69857 +- 0.00002 h). BO Cet and V380 Oph exhibit emission-line flaring with periodicities of 20 min and 47 min, respectively. The Halpha line of HL Aqr shows significant blueshifted absorption modulated at the orbital period. Similarly to the emission S-wave of the high-inclination SW Sex stars, this absorption S-wave has its maximum blue velocity at orbital phase ~0.5. We estimate an orbital inclination for HL Aqr in the range 19 < i < 27 deg, which is much lower than that of the emission-dominated, non-eclipsing SW Sex stars (i ~ 60-70 deg). This gives rise to the interesting possibility of many low-inclination nova-likes actually being SW Sex stars, but with a very different spectroscopic appearance as they show significant absorption. The increasing blueshifted absorption with decreasing inclination points to the existence of a mass outflow with significant vertical motion. This six new additions to the SW Sex class increase the presence of non-eclipsing systems to about one third of the whole SW Sex population, which therefore makes the requirement of eclipses as a defining criterion for SW Sex membership no longer valid. The statistics of the cataclysmic variable population in the vicinity of the upper period gap is also discussed.

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arXiv2006

The emission line galaxy TV Reticuli: Evidence for an ultraluminous supernova

TV Ret was classified as a cataclysmic variable due to an outburst observed in 1977. We intended to confirm this classification and derive some basic properties of the system. Low resolution optical spectra were obtained for a spectral classification of the object. We find that the object is not a cataclysmic variable but an emission line galaxy with a redshift z=0.0964. An R-image taken in very good seeing conditions shows that the object is extended. We show that TV Ret is a blue dwarf galaxy, probably compact, with an absolute magnitude of MB = -17.5, a metallicity of 0.12 solar, and an average temperature of 1.3 10^4 K. The line ratios place it among the HII galaxies, although close to the border of the Seyfert2s. The outburst, which was observed in 1977, could thus be explained by a supernova explosion. However, with an absolute magnitude around MB = -21, it was an extremely bright one.

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arXiv2006

AD Mensae: a dwarf nova in the period gap

AD Men was classified as a probable long-period dwarf nova based on its long-term variability. Recent spectroscopic data instead suggested a short-period system. With the here presented observations we aim at clarifying its nature. Time--resolved photometry and spectroscopy has been used to get information on the orbital period of this system. The light curve shows the typical flickering and a clear hump--like periodic modulation with an average amplitude of 0.3mag and a period of P=2.20(02)h. The radial velocity measurements of the Halpha emission line confirm this value as the orbital period. AD Men is thus located at the lower end of, but clearly inside, the gap of the period distribution of cataclysmic variables, making it one of only 11 dwarf novae in this important period range.

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arXiv2006

Spectroscopy of the candidate pre-CV LTT 560

We present preliminary results on spectroscopic data of the candidate pre-cataclysmic variable LTT 560. A fit to the flux-calibrated spectrum reveals the temperature of the white-dwarf primary to be T_eff = 7000 - 7500 K, and confirms the result of previous studies on the detection of an M5V secondary star. The analysis of radial velocity data from spectral features attributed to the primary and the secondary star shows evidence for low-level accretion.

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arXiv2005

Spectroscopic classification of cataclysmic variable candidates

We present low resolution optical spectroscopy for six cataclysmic variable candidates and the old nova V888 Cen. We confirm the classification as cataclysmic variable for LB 9963 and FQ Mon, while the other four candidates turn out to be different type of stars. We discuss the individual spectra and pay special attention to the mass transfer rate and disc temperature and density of the three cataclysmic variables.

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arXiv2005

Outbursts on normal stars. FH Leo misclassified as a novalike variable

We present high resolution spectroscopy of the common proper motion system FH Leo (components HD 96273 and BD+07 2411B), which has been classified as a novalike variable due to an outburst observed by Hipparcos, and we present and review the available photometry. We show from our spectra that neither star can possibly be a cataclysmic variable, instead they are perfectly normal late-F and early-G stars. We measured their radial velocities and derived the atmospheric fundamental parameters, abundances of several elements including Fe, Ni, Cr, Co, V, Sc, Ti, Ca and Mg, and we derive the age of the system. From our analysis we conclude that the stars do indeed constitute a physical binary. However, the observed outburst cannot be readily explained. We examine several explanations, including pollution with scattered light from Jupiter, binarity, microlensing, background supernovae, interaction with unseen companions and planetary engulfment. While no explanation is fully satisfactory, the scattered light and star-planet interaction scenarios emerge as the least unlikely ones, and we give suggestions for further study.

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arXiv2005

The star formation history of the LSB Galaxy UGC 5889

We present HST photometry of the LSB galaxy UGC 5889 and derive its recent star formation history. In the last 200 Myr the star formation proceeded in modest bursts at a rate of the order of e-2 to e-3 solar masses masses per year, with periods of extremely low SFR or even quiescence. The rate derived from the present study for the last 20 Myr is in agreement with the Halpha emission from the galaxy. The presence of a consistent population older than 200 Myr is suggested by the data. However, observational errors and completeness correction prevent any firm conclusion on the oldest age. The total mass of stars is of the order of 5.5e7 solas masses. Even if the recent episodes of star formation have heated the gas and carved a hole in the disk, blow-away of the gas is unlikely to occur.

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arXiv2004

Spectroscopic analysis of tremendous--outburst--nova candidates

In the course of a long-term project investigating classical novae with large outburst amplitudes, we have performed optical spectroscopy of several old-nova candidates. We here present the spectra of the candidates V630 Sgr, XX Tau, CQ Vel, V842 Cen, and V529 Ori, that hitherto lacked such classification. While the first four show typical spectra for cataclysmic variables, and can thus be identified as such, V529 Ori is probably misclassified. Of special interest are the two systems XX Tau and V842 Cen, which show all signs for being low mass transfer systems. As such they can be used to judge the evolution scenarios for novae. In particular, given the rather young age of their outburst, it appears more likely that these systems are not on their way into hibernation, (i.e., cutting off mass transfer for a longer period of time), but are simply settling down towards their original configuration of comparatively low, but steady, mass transfer, such as for dwarf novae.

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arXiv2004

First spectra of the W UMa system V524 Monocerotis

We present the first high-resolution spectra of the W UMa contact binary V524 Mon. The spectra of the two components are very similar, resembling a G5 and a K0. We find the radial velocities and rotational velocities consistent with corotation. We estimate the radii and the masses and derive a mass ratio M_2/M_1 = 2.1. We confirm that V524 Mon is a W-type contact system, likely enclosed in a common convective envelope, as found by Samec & Loflin (2003). We do not find evidence for the expected level of emission in the chromospheric CaII H and K lines, neither H_alpha, indicating that the magnetic activity is much weaker than expected or that other processes are hampering chromospheric emission.

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arXiv2003

Recovery of the old nova V840 Ophiuchi: A carbon rich system

We present optical spectroscopy and multi colour photometry of the old nova V840 Oph. We rediscovered the nova based on its position in the colour--colour diagrams. It stands out as a very blue object with an additional red component. We present the first optical spectroscopy of this candidate and confirm its nova character. Furthermore, V840\,Oph has been found as one of very few cataclysmic variables showing C IV emission at lambda = 580/1 nm. From the analysis of the carbon lines it seems probable that V840 Oph contains actually a carbon-rich secondary star. So far, only the nova-like QU Car has been known to have such a companion. We furthermore find spectroscopic evidence that V840 Oph has a hot, dense accretion disc or stream and is probably a magnetic system.

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arXiv2003

The emission distribution of RR Pictoris

We present time-resolved optical spectroscopy of the old nova RR Pic. Two emission lines (Halpha and He I) are present in the observed part of the spectrum and both show strong variability. Halpha has been used for Doppler tomography in order to map the emission distribution in this system for the first time. The resulting map shows the emission from the disc as well as two additional emission sources on the leading and trailing side of the disc. Furthermore we find evidence for the presence of either a disc-overflow or an asymmetric outflow from the binary with velocities up to +- 1200km/s. The origin of the outflow would be the emission source on the leading side of the accretion disc.

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arXiv2003

Dust and Molecules in V4743 Sgr

We present 1.2 mm continuum images and spectral line observations of CO(1--0) and SiO(3--2) rotational transitions of the recent nova V4743 Sgr. The nova is detected at 1.2 mm showing a variable millimetre emission. Only upper limits of T_A* = 0.06 K for CO and T_A* = 0.03 K for SiO could be derived. We discuss the results in terms the nature of the millimetre emission favouring dust from a phase before the recent outburst as the likely radiating source. We also comment on the possibility of free-free emission from the ionised shell as the source of the measured millimetre radiation.

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arXiv2001

The cataclysmic variable CW 1045+525: a secondary-dominated dwarf nova?

We present spectroscopic and photometric observations of the cataclysmic variable CW 1045+525. Both the optical spectrum and the photometric lightcurve show a strong contribution of a K5V - M0V secondary. We derive an orbital period P_orb = 0.271278(1) d by measuring the radial velocities of the absorption lines of the secondary. The period and spectral type of the secondary suggest a distance of 350 - 700 pc. There is evidence for additional sources of line- and continuum emission, but no direct evidence of an accretion disc. We discuss several scenarios for the nature of CW 1045+525 on the basis of our results, finding a dwarf nova classification the most probable, although not completely satisfying, explanation for the observed characteristics.

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arXiv2000

The bright 175um knots of the Andromeda Galaxy

Discrete far-infrared (FIR) sources of M31 are identified in the ISO 175um map and characterized via their FIR colours, luminosities and masses. With a mean size of 800pc, they probably represent several clouds in chance projection or giant cloud complexes. The 175um data point provides crucial information in addition to the IRAS 60 and 100um data: At least two modified Planck curves with temperatures of about 40K and 15-21K are necessary to fit the SEDs of the knots. We distinguish between three types of knots - cold, medium, warm - in order to recognize trends. Comparisons with radio and optical tracers show that - statistically - the cold knots can be identified well with CO and HI radio sources and thus might represent mainly molecular cloud complexes. The warm knots coincide with known HII regions and supernova remnants. The medium knots might contain a balanced mixture of molecular clouds and HII regions. The cold knots have a considerable luminosity and their discovery raises the question of hidden star formation. Though the optically dark dust lanes in M31 generally match the FIR ring, surprisingly we do not find a convincing coincidence of our knots with individual dark clouds which might therefore show mainly foreground dust features. The ratio of FIR luminosity to dust mass, L/M, is used to measure the energy content of the dust. The knots have a clear L/M excess over the rest of M31, providing evidence that they are powered by star formation in addition to the interstellar radiation field. The L/M ratio of the warm knots is comparable to that of Galactic HII regions like M42 or NGC2024, while that of the cold knots still reaches values like in the average Orion complex. Thus both the warm and the cold knots are interpreted as containing large cloud complexes with considerable ongoing star formation.

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arXiv2000

The Galactic disk: study of four low latitude Galactic Fields

We present deep V and I photometry of stellar field in four previously unstudied low latitude regions of the Galactic disk. All observed fields are located at the western side of the Galactic Center in the direction of the Coalsack-Carina region. Two of them are suspected to cross the inner spiral arm. More than $10^5$ stars are detected in total, down to a magnitude of V $\sim 23.5$. Due to the low galactic latitude of the studied fields, the scale length and mainly the scale height of the thick disk are not strongly constrained by the observations. However a thin disk scale height of about 250$\pm 60$ pc seems to be favored. The data are very sensitive to the star formation rate of the thin disk. A decreasing star formation rate (SFR) is necessary to reproduce the distribution of the stars in the colour-magnitude diagrams (CMDs) as well as the luminosity functions. A constant or a strongly increasing SFR as derived using Hipparcos data for the solar neighborhood (Bertelli et al 1999) are marginally in agreement with the luminosity functions but they are at odds with the CMDs. The analysis of these data suggest that the solar neighborhood SFR cannot be considered as representative for the whole thin disk. From the star-counts the local neighborhood mass density in stars more massive than 0.1 M$_\odot$ is found to be 0.036--0.02 M$_\odot$ pc$^{-3}$. Finally, the location of inner spiral arm is discussed. We find evidence of a population younger than 10$^8$ yr distributed in a spiral arm at a distance of 1.3$\pm 0.2$ and 1.5 $\pm 0.2$\,Kpc in the directions l$\sim$\,292 and l$\sim$\,305 respectively. This result is consistent with the spiral arm pattern defined on the basis of pulsars and young associations.

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